Tea products are most commonly available commercially in the U.S. as granular instant teas, or as ready-to-drink canned products. Liquid tea concentrates are sold primarily to food-service or institutional customers, rather than directly to the consumer. The concentrates, like instant tea, require the addition of water to prepare a tea beverage for consumption.
Acid-catalyzed degradation reactions occur, over time, in liquid tea products resulting in the development of off-flavor compounds and precipitates. The tea solids react with acid to form off-flavor and malodorous compounds. If sugar is present it can react with the acid in the tea to develop off-flavor volatiles such as furfural. Also, if lemon is present acid-catalyzed degradation of limonene to terpenes can occur.
These degradation reactions are limited in dry instant tea products due to the dry matrix but do occur in the beverages prepared by dissolving the instant tea in water. For liquid tea concentrates, the problem of degradation occurs prior to beverage preparation due to the liquid matrix and to the high concentration of the components. Those liquid tea mix concentrates currently available commercially avoid degradation reactions by omitting tea as a component. A tea essence or tea aromatics are substituted. Since no real tea solids are present, degradation reactions are limited.
Most of the liquid tea products commercially available contain preservatives to aid in preventing product degradation. Antimicrobial agents are commonly employed to assure product safety. Antioxidants are used to prevent or retard oxidative decomposition. After an extended period of time these preservatives lose effectiveness and can degrade into other compounds.
Except for the use of such additives, the current processes for the preparation of tea products make no provision for control or prevention of degradation reactions between tea product components. Prior art processes address primarily degradation reactions in the areas of microbial spoilage and oxidation reactions. Other possible degradation reactions appear to have received little attention. Typical tea processing includes the following steps: extraction of tea from tea leaves, precipitation of tannin-caffeine complexes (cream), separation of these precipitates, and concentration of the resulting clarified liquid. For instant products this is followed by dehydration, agglomeration, and aromatization. For example, see U.S. Pat. No. 2,891,865 of Seltzer et al., issued June 23, 1959. This patent discloses a process for preparing liquid tea concentrates and powders wherein tea is countercurrently extracted, and the volatiles are stripped and condensed to form an aroma concentrate. The creaming operation is carefully controlled with respect to tea solids, time, and temperature, to achieve a balanced concentration of tannins and caffeine. Finally, the aroma and decreamed concentrates are combined.
Two references disclose tea processing wherein acid is added to tea extract. U.S. Pat. No. 2,785,979 of Mitchell, issued Mar. 19, 1957, employs acidification to maximize tea solids in tea extracts. After a cold water extraction, the residual tea leaves are extracted with acidified hot water. The residue is then acidified to pH 4, heated, and autoclaved to remove additional soluble material from the cells of the leaves. The cold water, acidified hot water, and acidified autoclaved extracts are then combined. U.S. Pat. No. 1,854,062 of Potter et al., issued Apr. 12, 1932, acidifies hot tea extract, or tea extract after cooling, to coagulate the cream precipitates, thereby rendering them more filterable. It is recognized that acidification appears to cause further precipitation, but ease of separation of the precipitates is the object of the invention.
It is recognized by the prior art that sulfur groups can participate in degradation reactions. U.S. Pat. No. 3,519,441 of Ferrara et al., issued July 7, 1970, discloses a process for treating flour or starch to eliminate free SH groups. The flour or starch is heated to 220.degree. F. to 305.degree. F. (104.degree. C. to 152.degree. C.) and contacted with steam under pressure. This treatment chemically modifies the flour or starch so that no free SH groups are present. The treated flour or starch is storage-stable and does not become rancid.
Iced tea beverages prepared from currently available commercial tea products are stable for only a short time in the refrigerator. Even if preservatives are present, iced tea beverages will become turbid, usually within about one week, because the components interact in degradation reactions to form precipitates. Eventually off-flavors develop. Even the tea products that contain no tea develop a certain low level of turbidity and become cloudy in appearance. It is desirable for consumers to have a convenient product without preservatives containing tea which is shelf-stable. Clearly, it is advantageous for the beverage prepared from such a product to be stable and not develop off-flavors and precipitates upon storage in the refrigerator.
Accordingly, it is an object of this invention to provide a process for the preparation of a shelf-stable tea product.
It is a further object of this invention to provide a process for the preparation of a stable liquid tea concentrate or liquid tea mix concentrate which contains real tea without containing preservatives.
It is a further object of this invention to provide a process for the preparation of a liquid tea concentrate or liquid tea mix concentrate which does not develop off-flavors or off-aroma upon storage at room temperature.
It is a further object of this invention to provide a process for the preparation of tea products from which an iced tea beverage can be prepared that does not develop off-flavors upon storage.
It is a further object of this invention to provide a process for the preparation of tea products from which an iced tea beverage can be prepared that does not develop turbidity or precipitates upon storage.